The present invention relates to an input protection circuit suitable for use in an inductively coupled circuit or essentially any other type of electrical circuit.
There are many advantages to inductive coupling. One advantage is that inductive coupling allows additional opportunities for simple and efficient interoperability where devices can be used interchangeably. However, circuit designs that “cut the cord” and enable this interchangeability have the potential to make the circuit vulnerable to third party systems. That is, magnetic fields produced by third party systems may inadvertently energize the secondary coil in a remote device and provide an inappropriate amount of power. In some circumstances the power from these third party sources can be destructive. As wireless power becomes more widespread so too will the amount and variety of third party magnetic fields.
A variety of protection circuits are well known in wired applications. For example, fuses, circuit breakers, temperature sensors and current limiters are commonly used protection mechanisms to control some risks. Some of these components, like many other protection circuits, rely on an appropriate power source for operation. At times, an appropriate power source may not be available, such as may be the case in an inductively coupled environment.
Some protection circuits do not rely on an appropriate power source for operation. For example, a transient voltage suppressor (“TVS”) is one such protection circuit. A TVS is designed to react to sudden or momentary overvoltage conditions, such as those caused by lightning or motor arcing. A TVS operates by shunting excess current when the voltage exceeds an avalanche breakdown potential. A TVS is a clamping device that suppresses substantially all overvoltages above its breakdown voltage. Like most clamping devices, it automatically resets when the overvoltage goes away, but absorbs much of the transient energy internally. The transient energy is typically dissipated using a heatsink. However, if the overvoltage condition persists too long the TVS may break down, which could result in the circuit being damaged or destroyed.
Accordingly, it is desirable to provide a protection circuit that can protect a circuit from, among other things, persistent overvoltage conditions—even when an appropriate power source for the protection circuit is not available.